1. Field of the Invention
The present invention relates to a method, terminal device, and network device for providing redundancy parameters for an automatic repeat request processing at a terminal device of a communication network, particularly for uplink transmissions in a third generation mobile communication network.
2. Description of the Related Art
For wired links, reliability in data communications is traditionally obtained thanks to repetition. A packet is retransmitted when the previous attempt was unsuccessful. Such mechanism is called Automatic Repeat Request (ARQ). In the case of wireless transmissions, due to the poor quality of the link, packets should be protected against channel noise, fading due to mobility, and interference created by other users. Protection is mainly given by forward error coding (FEC), e.g. transmitting additional bits incorporated into the data packet. However, to provide the same quality as in a wired system, FEC overhead could lead to very inefficient transmissions. As a result, hybrid schemes, combining FEC and ARQ have been proposed. Hybrid ARQ (H-ARQ) has been defined as the joint use of ARQ and FEC. FEC provides correction of the most likely errors and thus avoids the conventional ARQ scheme to stall. On the other hand, ARQ could prevent FEC failure. Hence, the receiver may discard an erroneous transmission before decoding the new one. However, the decoder could benefit from previous attempts to improve the decoding performance of the current one. To achieve this, incremental redundancy schemes have been developed, where the first transmission is encoded with a high rate code, and thus low overhead but low protection, and the following transmissions simply consist of additional redundancy in order to decrease the code rate seen by the receiver.
Current enhancements for uplink packet data of Wideband Code Division Multiple Access (WCDMA) systems cover radio transmission of data from a mobile unit or mobile terminal, called User Equipment (UE) in third generation terminology, to a fixed station, called Node B in third generation terminology. Here, the case of erroneous reception of data packets is handled by Radio Link Control (RLC) signaling. This is disadvantageous in that a retransmission will require relatively large buffers and will introduce significant delays. One of the technologies under investigation in connection with enhanced uplink data is fast H-ARQ, where the packet retransmissions are handled at either physical layer or Media Access Control (MAC) layer and thus in principle at the Node B instead of the Radio Network Controller (RNC). This will significantly reduce the retransmission delay, allowing for more aggressive settings of the Block Error Rate (BLER) targets for the transmissions from the UE, which leads to a potential gain in uplink capacity through reduced signal-to-noise (Eb/N0) requirements.
During the standardization phase of High Speed Downlink Packet Access (HSDPA) for the Third Generation Partnership Project (3GPP) Release 5 specifications, the fast H-ARQ concept was introduced to the processing of the High-Speed Downlink Shared Channel (HS-DSCH), where the Node B has full control of the redundancy versions (RV) to be used for transmissions towards a given user, i.e., the standard simply specifies possible RVs but the Node B is free to use any RV and in any order. The Node B simply chooses the RV and signals the used RV to the UE on the High-Speed Shared Control Channel (HS-SCCH) just before the transmission of the data on the HS-DSCH using this RV. For the signaling of redundancy versions for HS-DSCH, three bits were assigned on the HS-SCCH, so that eight possible redundancy versions could be indicated.
Similarly, the simplest solution for RV selection for uplink transmissions would be if this selection was totally left to the UE. This may, however, cause problems in cases where different Node Bs have different capabilities which the UE should take into account. Moreover, the network may be operated in different ways, e.g. with high or low BLER target, which each may have different optimum RV strategies, such that only sub-optimal network performance is achieved. Further details regarding different redundancy versions and corresponding processing schemes can be gathered from the 3GPP specification TS 25.212.
Another problem in the uplink direction is that signaling from the UE to the Node B will introduce overhead from all UEs operating in the enhanced DCH mode. It is quite important that the RV coding information is received properly since an erroneous reception of these values will cause an erroneous reception of the data packet itself by introduction of erroneous puncturing patterns.